Silencing CHALCONE SYNTHASE in Maize Impedes the Incorporation of Tricin into Lignin and Increases Lignin Content

Abstract

Lignin is a phenolic heteropolymer that is deposited in secondary-thickened cell walls, where it provides mechanical strength. A recent structural characterization of cell walls from monocot species showed that the flavone tricin is part of the native lignin polymer, where it is hypothesized to initiate lignin chains. In this study, we investigated the consequences of altered tricin levels on lignin structure and cell wall recalcitrance by phenolic profiling, nuclear magnetic resonance, and saccharification assays of the naturally silenced maize (Zea mays) C2-Idf (inhibitor diffuse) mutant, defective in the CHALCONE SYNTHASE Colorless2 (C2) gene. We show that the C2-Idf mutant produces highly reduced levels of apigenin-and tricin-related flavonoids, resulting in a strongly reduced incorporation of tricin into the lignin polymer. Moreover, the lignin was enriched in b-b and b-5 units, lending support to the contention that tricin acts to initiate lignin chains and that, in the absence of tricin, more monolignol dimerization reactions occur. In addition, the C2-Idf mutation resulted in strikingly higher Klason lignin levels in the leaves. As a consequence, the leaves of C2-Idf mutants had significantly reduced saccharification efficiencies compared with those of control plants. These findings are instructive for lignin engineering strategies to improve biomass processing and biochemical production.

Silencing CAFFEOYL SHIKIMATE ESTERASE Affects Lignification and Improves Saccharification in Poplar

“…The tubes were vortexed and centrifuged at 14,000 rpm (20,000g) for 10 min, after which a 15-mL aliquot of the aqueous phase was injected on a UHPLC system (Waters Acquity UPLC) equipped with a BEH C18 column (2.1 3 150 mm, 1.7 mm; Waters) and hyphenated to a time-of-flight mass spectrometer (Synapt Q-Tof; Waters) using gradient elution. Gradient elution information, negative mode mass spectrometry setting, chromatogram integration, and alignment via Progenesis QI software (Waters) were performed as described previously (Eloy et al, 2017). Peak abundances were normalized to the dry weight (mg) of the pellet remaining after methanol extraction and dried in the SpeedVac.…”

Hydroxystilbene Glucosides Are Incorporated into Norway Spruce Bark Lignin

“…The flavone tricin was the first phenolic derived from outside the monolignol biosynthetic pathway to be implicated in lignification (del Río et al, 2012;Lan et al, 2015). Tricin was first discovered in lignin preparations from wheat (Triticum durum) straw (del Río et al, 2012), and further studies indicated that it is widely present in the lignins of all grasses as well as in other monocots (Rencoret et al, 2013;del Río et al, 2015;Lan et al, 2016aLan et al, , 2016b and can be manipulated biogenetically (Eloy et al, 2017;Lam et al, 2017). More recently, we also reported the occurrence in macaúba (Acrocomia aculeata), carnauba (Copernicia prunifera), and coconut (Cocos nucifera) palm fruit endocarps of a second class of polyphenolic compounds, hydroxystilbenes (piceatannol, resveratrol, and isorhapontigenin), that behave as authentic lignin monomers participating in coupling and cross-coupling reactions during lignification and becoming integrally incorporated into the lignin structure (del Río et al, 2017;Rencoret et al, 2018).…”

Grass secondary cell walls, Brachypodium distachyon as a model for discovery

“…CHALCONE SYNTHASE, a pivotal enzyme for flavonoids production, uses malonyl-CoA and p-coumaryl-CoA as substrates. Silencing this enzyme in maize resulted in strongly reduced levels of apigenin-related and tricin-related flavonoids, and also strongly reduced incorporation of tricin into the lignin polymer (Eloy et al, 2017). The effect of the flavonoid pathway on the production of cell wall tricin content was also demonstrated in rice (Lam et al, 2017(Lam et al, , 2019.…”